Patent GB-975575-A (GB)
Title: A device for the transfer of information between magnetic film elements
IPC: G11C19/08
Filed: 1961-08-31
Abstract: 975,575. Circuits employing bi-stable magnetic elements. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 31, 1961 [Aug. 31, 1960], No. 31377/61. Heading H3B. In a binary information transfer device which comprises a series of magnetic film elements having aligned easy axes of magnetization, and in which propagation of information is determined by the stray switching field of each element in association with selective conductor energization, the stray switching field is arranged to predominate at that end of each element which lies in the direction of propagation so that information transfer can take place only in one direction. The arrangement utilizes either wedge-shaped film elements, or shaped conductors which concentrate the switching field towards one end of elements of uniform thickness. The shaped conductors may either be parallel to the film elements and have a varying cross section, or their spacing from the elements may vary. The elements may also have non-uniform density. Two-clock systems. As shown in Fig. 1, separate wedge-shaped film elements 13-17 are deposited on a substrate 11 with their easy axes aligned in the direction 12. Two circuits A and B are provided which when energized by respective half-waves of alternating current switch the associated element groups 13, 15, 17 or 14, 16 to the hard direction. The halfwave clock pulses act alternately, and when a switched element relaxes from the hard to the easy direction of magnetization it takes up the magnetic state of the adjacent element having the larger adjacent edge dimension. In a modification, Fig. 5, two strip conductors provide the circuits A and B, the conductors being notched alternately so that the conductor portions effectively associated with the wedge film elements have different current densities. Thus the current density of conductor A is high for film element 57 and switches that element to the hard direction, and is low for element 58. The converse applies to conductor B which switches elements 56 and 58, for example. An alternative arrangement is shown in Fig. 6, in which the conductors A and B have alternate portions such as 65A, 64B adjacent the films which are linked together by non-effective webs 66A, 65B. Elements 71- 77 of uniform thickness are used in the Fig. 7 arrangement in which the conductors A and B are shaped so that their spacing over the length of each film element decreases. This has the effect of concentrating the field at one end of an element when switching to the hard direction of magnetization. Consequently, when the clock pulse in a conductor A or B decreases; each associated film element switches back to the easy direction along its length in the direction of information transfer, and therefore progressively acquires the magnetization of the preceding element. The same effect is obtained by the use of flat conductors A and B with tapered regions each corresponding to an element, Fig. 8. Logical circuits. A series of film elements may be used for logical operations. In Fig. 9, a reversal of 180 degrees causes a reversal of each magnetization vector and hence inversion of the information transferred from the upper to the lower limb. Reversal of direction without inversion is obtained in Fig. 10 in which a junction film element 99 is used. A junction element 107 is also used in Fig. 11 which is biased in the easy direction of magnetization by energizing a coil 108. With the bias flux directed to the left (as shown), the arrangement performs the logical operation AND on information advanced along the parallel branches 105, 106. With the bias flux directed to the right the logical operation is changed to OR. One-clock systems. In Fig. 13 wedge-shaped magnetic elements 113-118 are switched to the hard direction of magnetization by alternating current applied to a conductor 119. Alternate elements are partially biased in opposite hard directions by permanent magnets 120. During each half-cycle of the alternating switching current the hard direction bias fields of alternate elements such as 113, 115, 117 are neutralized, and the bias fields of the remaining elements are increased to cause complete hard direction switching. As the end of each halfcycle approaches, those elements which were completely switched to the hard direction take up the magnetic state, inclined to the easy direction as shown by vectors 122, of the elements immediately preceding. In a modification, Fig. 16, a notched conductor 140 may be used in association with film elements of uniform thickness. The permanent magnets may also be replaced by suitable conductors carrying constant currents. An alternative transfer device is shown in Fig. 17 in which wedge-shaped elements 151-155 are formed as a continuous magnetic film on a substrate 150. Otherwise a continuous magnetic film 161 of uniform thickness, Figs. 18 and 19, may be used in association with a non-parallel conductor 162. In both devices full-wave alternating current in a meander-shaped conductor 157 or 162 respectively applies a switching field which acts along the easy axis of the film. Due to the conductor arrangement the switching field acts in opposite directions in alternate elements. As the alternating switching field is not uniform along each element, it loses its effect progressively along each element in the direction of information transfer as the end of each half-cycle of current is approached. Each element is therefore able to progressively take up the magnetic state existing at the end of the preceding element by the process of domain wall movement. The pattern of information movement over a complete cycle of current is shown diagrammatically in Fig. 20, the arrows above the diagrams at times t 1  and t 3  representing the instantaneous directions of the switching field. Shifting register and ring counter. Construction as a shifting register is completed by the provision of input and output conductors adjacent the first and last elements respectively. As a ring counter the elements 181 are arranged in a ring as shown in Fig. 21, and for a oneclock system as in Figs. 17-19 have an associated switching conductor 180.